In a conventional Package-on-Package (POP) process, a top package is bonded to a bottom package. The top package and the bottom package may also have device dies therein. By adopting the PoP process, the integration level of the packages may be increased.
In an existing PoP process, the bottom package is formed first, which includes a device die bonded to a package substrate. A molding compound is then molded on the package substrate, wherein the device die is molded in the molding compound. The package substrate further includes solder balls formed thereon, wherein the solder balls and the device die are on a same side of the package substrate. The solder balls are used for connecting the top package to the bottom package. Accordingly, the heights of the solder balls need to be greater than the thickness of the device die, so that the top portions of the solder balls may protrude above the top surface of the device die, and above the top surface of the molding compound. Accordingly, the sizes of the solder balls are also large, and the number of the solder balls that can be used in a PoP structure is limited.